TH 2.2 is a cloned hybrid cell line (Lymphoma X B-lymphocyte) which is induced by bacterial lipopolysaccharide (LPS) to a reduced rate of growth and to the secretion of cytokines, including IL-3, IL-6 and GM-CSF. Individual clones obtained in the presence of LPS are very heterogeneous with respect to size, and to the number and amounts of products secreted. Almost all clones return to the parental phenotype. We studied the effects of treatment with LPS and with cytokines on the behavior of TH2.2 during induction. Pretreatment of cells with LPS prior to induction produced profound unresponsiveness to LPS: Inhibition of growth and induction of cytokine secretion was blocked. This state of "tolerance" was very long lasting, even after treated cells were permitted to grow in regular growth medium in the absence of LPS. Secretion of GM-CSF was still very suppressed after 28 passage generations; secretion of IL-3, IL- 6 had recovered by this time, although it had been suppressed in passages 1-17. Cells were still partly resistant to the growth-inhibiting effects of LPS at passage 28. Thus, treatment with LPS produces unresponsiveness to its own action, as measured by four functional parameters, and each of the parameters recovers at a different rate. Pretreatment of TH 2.2 with TNF-alpha, IFN-gamma, IL-1, and IL-4 could effect the magnitude of the response to LPS by enhancing the secretion of GM-CSF and/or reducing the secretion of IL-3 to subsequent challenge with LPS.